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Retina is affected by amblyopia
New method of examining the retina may improve diagnosis and treatment of many diseases.
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BALTIMORE - A new method of examining the retina has detected previously unseen abnormalities in people with amblyopia and may lead to improved treatments, according to Kelly Hutcheson, MD, assistant professor of ophthalmology at the University of Maryland School of Medicine here.
Although earlier Nobel Prize-winning research by David Hunter Hubel and Tolsten Nels Wiesel in 1981 showed there was clearly a change in the brain's response to the amblyopic eye, "This is one of the first times we have seen such clear-cut changes in the retina in patients with amblyopia. This is really something people questioned until this time," Dr. Hutcheson said.
Multifocal electroretinogram
According to co-researcher Mary A. Johnson, PhD, the new test, the multifocal ERG (MERG), allows for a precise measurement of signals from various parts of the retina. Dr. Hutcheson reports that there are marked abnormalities detected by MERG in retinal ganglion cells of amblyopic eyes.
MERG is a system developed by Erich Sutter, PhD, of San Francisco and measures 103 points in the central 60° of the retina simultaneously, said Dr. Johnson, who is an associate professor of ophthalmology at the University of Maryland School of Medicine.
Multifocal refers to the use of a small, limited area in the retina as opposed to the entire field, she added.
"The patient looks at an array of black-and-white hexagons. The stimulus occurs when a hexagon changes from black to white or white to black while the shape remains the same. With changes occurring every 13.3 milliseconds, the contact lens the patient wears transmits the electrical potential generated in the nerves of the retina, in response to those scintillating hexagons, to a computer programmed with the stimulus sequence, known as an M-sequence. The computer does the auto correlation and prints out a map of the data," Dr. Johnson continued.
In the study performed by Drs. Hutcheson and Johnson, 20 adult patients had their amblyopic eyes compared to their healthy eyes. Patients with a visual acuity of 20/50 or worse showed a reduced response to light on the MERG test, indicating an abnormality. No changes were detected in patients with better than 20/50 acuity or those without amblyopia.
Patients in the study had a history of amblyopia for their entire lives. Residual changes caused by amblyopia were found in their eyes.
Treatment
Treatment for the condition has been limited to placing a patch on the good eye or using atropine drops to blur the vision in the sound eye.
"There's a national study going on right now to compare those two methods of treatment, but neither one is uniformly effective," Dr. Hutcheson said.
The national study is funded by the National Eye Institute of the National Institutes of Health and has nothing to do with the Hutcheson-Johnson investigation.
Dr. Hutcheson said her study might lead to other treatments.
"It is our hope in this study that if we can identify the mechanisms that are affecting the retina, we may be able to offer additional insights as to medication or therapy - these treatments would not necessarily be surgical, but maybe pharmacologic or other manipulations that we can offer to young children while they're being treated for amblyopia that may enhance their responsiveness to treatment," she concluded.
For Your Information:
- Kelly Hutcheson, MD, and Mary A. Johnson, PhD, can be reached at 419 W Redwood St., Suite 420, Baltimore, MD 21201-1595; (410) 328-5746; fax: (410) 328-1178. Dr. Hutcheson and Dr. Johnson do not have a direct financial interest in any of the products mentioned in this article, nor are they paid consultants for any company mentioned.